Becca, since you're on your parents medical insurance too I think you have to start "softer" with something like, "I need your help but I'm feeling very vulnerable about it and would appreciate it if we didn't have to talk to much about it right at first. . ." and just say you want to start therapy and will need (in the future) rides to and from sessions and maybe even think about asking if there are any better "times" for her or your father so when you make appointments you take their needs into account too.

I would make try to accent that you want to learn how to do things on your own rather than that you don't want your mother's help. It is a subtle difference but your mother does know something about therapy/therapists and is bound to offer; I think we want our mother's to care? and I would try to, as much as I was able, to not hurt her feelings and go out of the way to not make it sound like "I need your car-driving abilities but not you."

I always got tangled up with my stepmother because I took all her questions as attacks, even when they were genuine questions. I had a very hard time (and still do) with my T since T's want to make sure they understand well but I would think she was trying to "trick" me as my stepmother had.

I would let your mother ask questions; you don't either have to know the answers yet or let her "take over." You can keep making "I" statements to the effect, "I haven't worked on that yet" or "I don't feel comfortable discussing that with you right now. Right now I need help with getting a ride to and from a therapy session, do you have any better or worse times or days of the week I should keep in mind when I make the appointment?" Or you can keep answers "factual" but brief, "I want to talk to someone about how my foot operations are affecting me" or, "I need help with figuring out my future away from my mommy and daddy" and give a rueful smile so she should know not to take it personally that you won't talk to her :-)